The objectives of the present investigation are to determine whether low dosage X-irradiation (1-40 rad) will induce behavioral and functional alterations in rats exposed in utero, and, to correlate such behavioral and functional modifications with neuropathologic changes in the neonatal adult offspring. A preselected testing procedure will be utilized which incorporates classical teratologic studies, postnatal developmental markers, neonatal reflex tests, and adult behavioral analyses. Data acquistion will include: a) fetal developmental parameters, b) postnatal developmental parameters, and c) prenatal and postnatal functional and morphologic development of the central nervous system. The protocol consists of exposure of rats to 0, 1, 10, 20, or 40 rad of X-irradiation on days 9 or 17 of gestation. Half of the animals will be killed on the 22nd day. Standard teratologic evaluations will be completed, including complete dissection of all fetuses. The remaining rats will be allowed to deliver their litters. Five reflex tests and 2 physiological parameter tests will be initiated on postnatal day 3, and 5 adult behavioral tests will begin on day 60. Several histopathologic techniques will be employed to correlate functional changes with alterations in neocortical, allocortical, and cerebellar cortical morphology, including axonal alterations, dendritic size, shape, and branching patterns, and cell size, shape, location, and density. The present investigation will permit the evaluation of the effects of low dosage prenatal X-irradiation (non-teratogenic by classic analysis) on postnatal psychophysiologic development and function and correlation with possible neuropathologic alterations.